The chief executive of the troubled Co-op Bank has written to customers thanking them for "standing by us" during some of the "most difficult times".

Niall Booker's letters, addressed to individual named customers, landed on doormats this weekend.

Mr Booker said the bank has strengthened its capital position and management team and has a business plan intended to restore "longer-term sustainable profitability". But he said "delivering" the plan remains "challenging".

Last year the bank admitted it was losing customers as its reputation suffered following financial turmoil and a drugs scandal involving former chairman Paul Flowers.

A rescue plan to plug a £1.5 billion hole in finances was approved in December.

"I wanted to write to you personally to thank you for standing by us during some of the most difficult times in our history," says Mr Booker, in his letter.

"I am pleased to say we have strengthened both our capital position and management team. We have also put in place a business plan which we intend will restore us to longer-term sustainable profitability over time."

He added: "Whilst delivering our plan remains challenging, I hope I have given you a sense of the steps we have taken both to strengthen the business and begin to reward the faith you have shown in us."